Study findings updated . AI-assisted evidence summary, not individual medical advice or a clinician endorsement.
THE SHORT VERSION
What’s worth knowing.
The key findings, what they mean, and the context that matters.
THE HEADLINE TAKEAWAY1 in 5 had only a rash21% of COVID-positive survey respondents with a rash had no other symptom
For some people, a skin rash was the only sign of COVID-19.
Among UK users of a COVID symptom app, 8.8% of those who tested positive reported skin changes, and rashes were linked to a positive swab (odds ratio 1.67, meaning higher odds). In a separate online survey of people with rashes who tested positive, 17% said the rash came first and 21% said it was the only sign of COVID-19.
A new rash, even without fever or cough, can be an early clue to COVID-19. Skin signs may flag infections that standard symptom checklists would miss. Self-reported app and online-survey data from the UK in 2020, mostly from white users; survey respondents chose to report their rashes.
See the evidence
Analysis of 336,847 UK users of the COVID Symptom Study app plus an online survey of 11,544 people about skin rashes, spring 2020.
From the study: “Using data from the app, we show significant association between skin rashes and a positive swab test result (odds ratio 1·67, 95% confidence interval 1·42-1·97).”
1 in 5 had only a rash
Visconti A et al. Diagnostic value of cutaneous manifestation of SARS-CoV-2 infection. The British journal of dermatology. 2021.
From the study: “we found that 17% of SARS-CoV-2-positive cases reported skin rashes as the first presentation, and 21% as the only clinical sign of COVID-19.”
1 in 5 had only a rash
Visconti A et al. Diagnostic value of cutaneous manifestation of SARS-CoV-2 infection. The British journal of dermatology. 2021.
Hair loss was the second-strongest lasting symptom after COVID-19 without hospitalization.
4.0× hair loss riskHazard ratio 3.99 vs matched adults with no recorded infection, after 12 weeks
UK primary-care records compared 486,149 non-hospitalized adults with confirmed COVID-19 against 1,944,580 matched adults with no recorded infection. After 12 weeks, hair loss was recorded at about 4.0 times the rate (hazard ratio 3.99), second only to loss of smell among the symptoms studied.
Hair shedding months after an infection that never needed hospital care shows up as a clear pattern in millions of medical records, not just anecdotes. People who notice it are describing something the records also show. Observational study of UK GP records from January 2020 to April 2021; it relies on symptoms people reported to doctors and cannot prove cause.
See the evidence
Matched cohort study of UK primary-care records: 486,149 non-hospitalized adults with COVID-19 and 1,944,580 matched adults without recorded infection, tracking 115 symptoms.
From the study: “We selected 486,149 adults with confirmed SARS-CoV-2 infection and 1,944,580 propensity score-matched adults with no recorded evidence of SARS-CoV-2 infection.”
4.0× hair loss risk
Subramanian A et al. Symptoms and risk factors for long COVID in non-hospitalized adults. Nature medicine. 2022.
Adults 50 and older had more shingles in the months after COVID-19.
15% higher shingles riskAdults 50+ with vs without COVID-19 (adjusted incidence rate ratio 1.15)
In US insurance records, adults 50 and older diagnosed with COVID-19 had a 15% higher rate of shingles (a painful, blistering rash from reawakened chickenpox virus) than matched adults never diagnosed, and 21% higher after a COVID hospital stay. No extra risk appeared after day 183 (about 6 months), and in the older age group the rise was not statistically significant.
Shingles is painful; knowing that risk rose for months after COVID-19 can help older adults and their doctors recognize it sooner. Observational US claims study covering 2020 to early 2021; it cannot prove cause, and the authors note some COVID-19 cases were likely missed.
See the evidence
Matched cohort study of US commercial and Medicare-supplement insurance claims: 394,677 adults aged 50+ with COVID-19 and 1,577,346 matched adults without it.
From the study: “≥50-year-olds diagnosed with COVID-19 had a 15% higher risk of developing HZ than those without COVID-19 (aIRR, 1.15; 95% CI, 1.07–1.24; P < .001)”
15% higher shingles risk
Bhavsar A et al. Increased Risk of Herpes Zoster in Adults ≥50 Years Old Diagnosed With COVID-19 in the United States. Open forum infectious diseases. 2022.
From the study: “The increased HZ risk was more pronounced (21%) following COVID-19 hospitalization (aIRR, 1.21; 95% CI, 1.03-1.41; P = .02).”
15% higher shingles risk
Bhavsar A et al. Increased Risk of Herpes Zoster in Adults ≥50 Years Old Diagnosed With COVID-19 in the United States. Open forum infectious diseases. 2022.
From the study: “No increased HZ risk was seen in COVID-19 patients after day 183”
15% higher shingles risk
Bhavsar A et al. Increased Risk of Herpes Zoster in Adults ≥50 Years Old Diagnosed With COVID-19 in the United States. Open forum infectious diseases. 2022.
Hair loss after COVID-19 usually resolved, with median recovery near five months.
95% of cases resolvedResolution rate among 58 published cases of post-COVID hair loss
A review found most post-COVID hair loss was telogen effluvium, a temporary shedding phase triggered by illness. Across 58 individually reported cases, mostly women (82.8%), shedding began a median of 2.0 months after COVID-19, recovery took a median of 5.0 months, and 95% resolved. There was no clear link between COVID-19 severity and how much hair was lost.
Losing hair after an illness is frightening, but this kind of shedding mostly reverses. Knowing the usual timeline can spare people panic while they wait. Scoping review whose recovery figures rest on just 58 published case reports; the authors call the overall evidence uncertain and lacking strength.
See the evidence
Systematic scoping review of 26 published articles through November 2021, including 58 individually described cases of hair loss after COVID-19.
From the study: “Analysis of the 58 cases also found similar results with most of the cases being female (82.8%)”
95% of cases resolved
Czech T et al. Characteristics of hair loss after COVID-19: A systematic scoping review. Journal of cosmetic dermatology. 2022.
From the study: “the median onset of hair loss of 2.0 months, and the median time to recovery of hair loss of 5.0 months with a resolution rate of 95%”
95% of cases resolved
Czech T et al. Characteristics of hair loss after COVID-19: A systematic scoping review. Journal of cosmetic dermatology. 2022.
Chilblains rose in the pandemic, yet few patients actually tested positive.
1 in 27 tested positive17 of 456 tested chilblains ('COVID toes') patients had a positive COVID test
In Kaiser Permanente Northern California, chilblains (painful red-purple patches on toes or fingers, dubbed 'COVID toes') rose during the pandemic but tracked only weakly with local COVID-19 rates. Of 456 tested chilblains patients, only 17 (3.7%) were positive. The authors say more care-seeking or shelter-in-place behavior changes could also explain the rise.
Early reports made 'COVID toes' sound like a telltale sign of infection. Population data suggests the link is weaker than it first appeared, so painful toes alone are not proof of COVID-19. Observational records study in one northern California health system, 2016–2020; not every patient was tested, and a weak correlation cannot show cause.
See the evidence
Retrospective cohort study of Kaiser Permanente Northern California members comparing chilblains rates from 2016 through 2020, including 780 pandemic-era cases.
From the study: “However, only 17 of 456 (3.7%) patients with chilblains tested during the pandemic were positive for SARS-CoV-2”
1 in 27 tested positive
McCleskey PE et al. Epidemiologic Analysis of Chilblains Cohorts Before and During the COVID-19 Pandemic. JAMA dermatology. 2021.
From the study: “the incidence of chilblains increased during the pandemic but was correlated weakly with the incidence of COVID-19 across 207 location-months.”
1 in 27 tested positive
McCleskey PE et al. Epidemiologic Analysis of Chilblains Cohorts Before and During the COVID-19 Pandemic. JAMA dermatology. 2021.
From the study: “These findings may have resulted from a causal role of COVID-19, increased care-seeking by patients with chilblains during the pandemic, or changes in behavior during shelter in place.”
1 in 27 tested positive
McCleskey PE et al. Epidemiologic Analysis of Chilblains Cohorts Before and During the COVID-19 Pandemic. JAMA dermatology. 2021.
Fewer than half of vaccine skin reactions returned at the second dose.
43% reacted again29 of 67 people with a first-dose skin reaction reacted again after the second dose
A US registry gathered skin reactions to Moderna and Pfizer shots, most often 'COVID arm': a red, itchy, swollen patch near the injection, with delayed large local reactions starting a median of 7 days after vaccination. Of 67 people with a first-dose skin reaction, 29 (43%) reacted again after the second dose. None had anaphylaxis (severe allergic reaction) or another serious problem after it.
A skin reaction to the first shot often did not repeat, and repeats here were not dangerous. That can ease worry about finishing a vaccine series after an itchy arm. Doctor-reported registry from December 2020 to February 2021, mostly US women; the authors note it cannot measure how often reactions occur.
See the evidence
Registry of 414 skin reactions reported by US health workers after Moderna or Pfizer vaccination, December 2020 to February 2021.
From the study: “Therefore, of the 67 patients who had a cutaneous reaction to the first dose, 29 (43%) also had a cutaneous reaction to the second dose.”
43% reacted again
McMahon DE et al. Cutaneous reactions reported after Moderna and Pfizer COVID-19 vaccination: A registry-based study of 414 cases. Journal of the American Academy of Dermatology. 2021.
From the study: “No patient experienced anaphylaxis or another severe adverse event after the second COVID-19 vaccine dose.”
43% reacted again
McMahon DE et al. Cutaneous reactions reported after Moderna and Pfizer COVID-19 vaccination: A registry-based study of 414 cases. Journal of the American Academy of Dermatology. 2021.
From the study: “delayed large local reactions occurring median 7 days (IQR 7-8) after vaccination”
43% reacted again
McMahon DE et al. Cutaneous reactions reported after Moderna and Pfizer COVID-19 vaccination: A registry-based study of 414 cases. Journal of the American Academy of Dermatology. 2021.
Fewer melanomas were diagnosed in 2020, and those found were more advanced.
15.5% drop in diagnosesMelanoma diagnoses in 2020 vs prior years in the US SEER cancer registry
In the US SEER national cancer registry, melanoma diagnoses fell 15.5% in 2020 compared with prior years, which the authors say may reflect delayed visits. People diagnosed in 2020 had thicker, more often ulcerated (open-sore) and later-stage tumors. With short follow-up so far, this was not linked to worse survival.
Skin cancers caught later are harder to treat. Delayed skin checks during the pandemic may have let some melanomas grow before they were found. Retrospective US registry study of melanomas diagnosed 2018–2020; the authors note short follow-up means survival effects may not show yet.
See the evidence
Population-based study of the US SEER cancer registry comparing invasive skin melanomas diagnosed in 2018–2019 with those diagnosed in 2020.
From the study: “There was a 15.5% drop in melanoma diagnosis in 2020 compared to prior years, which could relate to delayed presentation.”
15.5% drop in diagnoses
Xiong DD et al. The impact of the COVID-19 pandemic in 2020 on the diagnosis, treatment, and outcomes of invasive cutaneous melanoma: A retrospective national cohort study. Journal of the American Academy of Dermatology. 2023.
From the study: “Patients diagnosed with melanoma in 2020 tended to have thicker, more ulcerated, and more advanced tumors, but this was not associated with survival.”
15.5% drop in diagnoses
Xiong DD et al. The impact of the COVID-19 pandemic in 2020 on the diagnosis, treatment, and outcomes of invasive cutaneous melanoma: A retrospective national cohort study. Journal of the American Academy of Dermatology. 2023.
From the study: “This is a retrospective cohort review and limited by short follow-up times, which could affect survival outcomes.”
15.5% drop in diagnoses
Xiong DD et al. The impact of the COVID-19 pandemic in 2020 on the diagnosis, treatment, and outcomes of invasive cutaneous melanoma: A retrospective national cohort study. Journal of the American Academy of Dermatology. 2023.
Psoriasis patients on biologics were hospitalized for COVID-19 less often.
17% hospitalizedPsoriasis patients on biologics; 34% on non-biologic systemic drugs
In an international doctor-reported registry of people with psoriasis and COVID-19, 17% of those on biologics (injected drugs aimed at specific immune signals) were hospitalized, versus 34% of those on non-biologic systemic (whole-body) drugs. Overall, 93% fully recovered, and different biologic types showed no significant differences.
Many people with psoriasis worry that immune-targeting drugs make COVID-19 more dangerous. In this registry, biologic users did not fare worse, though the design cannot show the drugs protect. Doctor-reported case series of 374 patients from 25 countries; the authors warn of possible selection bias and unmeasured confounding.
See the evidence
International registry of 374 psoriasis patients with confirmed or suspected COVID-19, reported by clinicians in 25 countries.
From the study: “among patients receiving biologic therapy for their psoriasis (≤4 weeks before COVID-19 onset; 44 of 265 [17%]) than among those receiving nonbiologic systemic therapy (22 of 65 [34%])”
17% hospitalized
Mahil SK et al. Factors associated with adverse COVID-19 outcomes in patients with psoriasis-insights from a global registry-based study. The Journal of allergy and clinical immunology. 2021.
From the study: “In all, 348 patients (93%) were fully recovered from COVID-19, 77 (21%) were hospitalized, and 9 (2%) died.”
17% hospitalized
Mahil SK et al. Factors associated with adverse COVID-19 outcomes in patients with psoriasis-insights from a global registry-based study. The Journal of allergy and clinical immunology. 2021.
From the study: “No significant differences were found between classes of biologics.”
17% hospitalized
Mahil SK et al. Factors associated with adverse COVID-19 outcomes in patients with psoriasis-insights from a global registry-based study. The Journal of allergy and clinical immunology. 2021.
Hair shedding began weeks after a positive test in selected cases
Among COVID-associated telogen-effluvium cases, hair shedding began an average 53.76 days after a positive SARS-CoV-2 PCR test.
Cases came from a selected 204-patient cohort with infection in the preceding three months; study published in 2021. The onset average is for the hair-shedding cases, not all participants or the wider population.
Study details & original results
Aksoy, Hasan et al.. COVID‐19 induced telogen effluvium.. Dermatologic Therapy. 2021.
Onset timing among COVID-19-associated telogen-effluvium cases within a selected 204-patient cohort with SARS-CoV-2 infection in the preceding three months (study published in 2021); not population prevalence.
Mean 53.76 (± 23.772) days after SARS-CoV-2 RT-PCR positivity
Onset timing among COVID-19-associated telogen-effluvium cases within a selected 204-patient cohort with SARS-CoV-2 infection in the preceding three months (study published in 2021); not population prevalence.
Added
Mean 53.76 (± 23.772) days after SARS-CoV-2 RT-PCR positivitySource [1]
Browse the 9 original sourcesThe complete bibliography behind this monitor.
[1]
Aksoy, Hasan et al.. COVID‐19 induced telogen effluvium.. Dermatologic Therapy. 2021.
Bhavsar A et al. Increased Risk of Herpes Zoster in Adults ≥50 Years Old Diagnosed With COVID-19 in the United States. Open forum infectious diseases. 2022.
McMahon DE et al. Cutaneous reactions reported after Moderna and Pfizer COVID-19 vaccination: A registry-based study of 414 cases. Journal of the American Academy of Dermatology. 2021.
Xiong DD et al. The impact of the COVID-19 pandemic in 2020 on the diagnosis, treatment, and outcomes of invasive cutaneous melanoma: A retrospective national cohort study. Journal of the American Academy of Dermatology. 2023.
Mahil SK et al. Factors associated with adverse COVID-19 outcomes in patients with psoriasis-insights from a global registry-based study. The Journal of allergy and clinical immunology. 2021.
Read each original paper for its complete methods, population and limitations. Different studies can ask different questions and report different kinds of results. Dates marked “added” describe when a finding entered this monitor, not when the study was published or clinically reviewed.
Download the findings and bibliography displayed in this page snapshot. Values and confidence intervals remain as reported text; this is not a pooled estimate or a systematic review. Product-label observations and editorial takeaways are excluded.
These findings may omit evidence or contain errors and have not been reviewed by a clinician. A citation or download does not establish source verification. Read the original studies for their methods and limitations.
The October 2026 COVID citation audit found errors in this collection. These downloads may still contain affected findings and bibliography entries. Read the correction record before using them.
“Added” dates record entry into the monitor, not publication or clinical review. A null original acquisition or derivation means its historical record is unknown; a current record or verification has its own observation time. The SHA-256 snapshot identifier binds the downloadable public fields. CSV includes finding rows and bibliography-only source rows; JSON includes both lists. Spreadsheet-sensitive CSV cells begin with an apostrophe for safety; JSON preserves the original text.
For attribution, cite ModernDoc and the page URL, data update date and snapshot identifier in the download. Original studies retain their own rights; this download does not grant a licence to their full text.